1. The Field of the Invention
The present invention relates generally to mechanical transmission devices. More particularly, it concerns a mechanical jack transmission which incorporates a single gear rack and pinion gear system for lifting or lowering a load.
2. The Background Art
Mechanical lifting jacks are known in the prior art for lifting vehicles and other loads. One of the principal aspects of every mechanical jack is the transmission mechanism by which an external applied force is transmitted to the load to be lifted.
Some prior art mechanical jacks are specially designed for high lifting. Such jacks often involve one or more gear racks with rotational gearing disposed in meshing engagement with the gear rack. The prior art designs involving gear racks are characterized by the disadvantage that unsafe backspin may occur during operation of the jack, causing the load carrier to plummet rapidly downward under the force of the load and thereby posing a serious risk of damage and injury. Some of the high-lift jacks have utilized spring-loaded pawl devices to solve the problem of unsafe backspin, while others have introduced additional gearing. Either solution introduces unneeded complexity and expense to the jack.